Mollic Epipedon Research Articles

Correspondence of Soil Properties and Classification Units with Sagebrush Communities in Southeastern Oregon: II. Comparisons within a Multi‐taxa Soil‐vegetation Unit

AbstractA complex soil landscape composed of two dominant soil components supporting a range of heterogeneous sagebrush communities was examined in order to determine if soil properties and classification differed among plant community types. Cluster analysis of 64 vegetation samples identified six recurring plant groupings (RPGs). Properties of RPG soil profiles were statistically compared by defining aggregate horizons (tiers) that were common to all profiles. Recurring plant groupings were characterized by relative canopy cover of Artemisia arbuscula, Artemisia tridentiata ssp. wyomingensis, Festuca idahoensis, Agropyron spicatum; total grasses, and total herbs. Stepwise discriminant analysis selected thickness of mollic epipedon, surface rock fragment cover, and thickness and weighted average dry consistence of the argillic horizon as those that best distinguished between RPG associated soils. Evidence suggests that series separations are justified based on family and class distinctions of higher categories or differences in range of one or more soil properties, including (i) horizon sequence, (ii) mollic epipedon thickness, (iii) structure of BAt subhorizon, (iv) thickness, and (v) weighted average dry consistence of the argillic horizon. Phase level separations of RPG associated soils from identical families are feasible if both physiographic and soil surface criteria are utilized together.

Influence of Climatic Conditions on Production of Stipa-Bouteloua Prairie over a 50-Year Period

Range forage yields obtained over a W-year period at the Research Substation near Manyberries in southeastern Alberta were analyzed in relation to several climatic factors. The basic variables were precipitation, pan evaporation, temperature, hours of sunlight, and wind velocity. The precipitation from April through July was highly correlated with range forage production and this relationship could be utilized to predict the annual forage production by 1 August each year. A slightly better correlation wns obMned when range forage production was related to the total of the previous September plus the current April through July preeip itation. Pan evaporation totals, mean temperature, and hours of sunlight were negatively correlated with forage production, while wind velocity during the growing season showed a low relationship to forage production. Stepwise regression analysis showed that the inclusion of May and June mean temperatures with June and July precipitation accounted for 63% of the variation in range forage production. The predicted forage yield would be useful in making management decisions or adjustments, especially during drought periods, while the long-term forage yield data can be utilized in range forage models or in validating their effectiveness. Studies on the response of mixed prairie to weather and climatic fluctuations have been mostly concerned with changes in floristic composition, with less attention to the relationship between climatic variations and range forage yields. Such relationships could provide ranchers with some method of predicting suitable stocking rates on native rangelands and aid ecologists in understanding short-term and long-term rangeland ecosystem dynamics. The relationship between precipitation ahd yield of range vegetation was investigated as early as 1922 in north-central Montana by Patton (1927). More recent studies by Rogler and Haas (1947) in North Dakota, Smoliak (1956) in southeastern Alberta, Rauzi (1964) in Wyoming, Hulett and Tomanek (1969) in western Kansas, and Ballard (1974) in Montana explored the relationship between precipitation during the growing season and range forage yields. The good correlations that they found could be utilized to predict seasonal range forage production as early as 1 July. Other studies showed that fall-through-summer precipitation better explained the variation in total forage production but spring precipitation best predicted grass production (Noller 1968, Whitman and Haugse 1972). Range forage production has also been related to soil type. In a study of 14 sites, Cannon (1983) found that thickness of mollic epipedon of range soils was significantly related to forage production and that using thickness and mean annual precipitation improved the estimate of range forage production. Weather fluctuations on Mixed Prairie grassland in the Northern Great Plains were shown to result in a dominance of xeric species during drought periods and mesic species under more favorable growing conditions (Coupland 1958,1959). Provision of more favorable growing conditions through weather modification may be a possibility with cloud seeding to increase precipitation. Hausle (1972) concluded that the amount of forage production that could result from additional precipitation could be predicted by statistical methods where long-term production and climatological data are available. Ballard and Ryerson (1973) indicated that increased precipitation resulting from weather modification will probably have a significant effect on range forage production only when combined with good livestock and grazing management

Morphology of Late Holocene Soils at the Lubbock Lake Archeological Site, Texas

AbstractThree soils have been identified in late Holocene deposits at the Lubbock Lake site, a well‐ stratified archaeological locality on the Southern High Plains. The soils have been informally named and their ages firmly established by radiocarbon dating. The soils formed in quartzose, sandy loam to sandy clay loam, dominantly eolian sediments with illite and mixed‐layer illite‐smectite clay mineralogy and lesser amounts of smectite and kaolinite. The Lubbock Lake Soil formed in material deposited between 5000 and 4500 yr BP and has had 4500 yr to form or, where buried, 3500 yr. The soils exhibits mollic and ochric (buried) epipedons, cambic and argillic and, in some positions, a partically gleyed B horizon, and Stage I or II, often multiple, calcic horizons. It is classified as either a Calciustoll, Haplustoll, Haplustalf, or Ustochrept. The Apache Soil formed in sediments deposited from 800 to 450 yr BP and is 450 yr old where not buried and 200 yr old where buried. The soil usually has a mollic epipedon but in some buried situations it is ochric. The B horizon is normally cambic but sometimes qualifies as argillic. Secondary carbonate accumulation, sometimes qualifying as calcic, commonly attains a Stage I morphology. The Apache Soil is classified as either an Ustochrept, Haplustoll, Calciustoll or possibly minimally developed Haplustalfs. The Singer Soil formed in sediments deposited from 250 and 100 yr. BP, allowing 100 yr for soil formation. The soil has an ochric epipedon and either a C, Bw, or a cambic horizon. Weak Stage I carbonate horizons are common but never qualify as calcic. The Singer Soil is classified as an Ustorthent. These three soils define a chronosequence that will allow a study of pedogenesis in Holocene sediments in a semiarid environment. The discovery of soils elsewhere on the southern High Plains of similar age, parent material, and landscape setting to the Lubbock Lake Soil and possibly the two younger soils, indicate that these late Holocene soils will be useful stratigraphic markers and dating tools.

Estimating Production of Range Vegetation from Easily Measured Soil Characteristics

AbstractVegetation production information is essential to rangeland management. Making range production estimates based on harvest data is expensive and time consuming. Few native range sites in Montana or comparable areas have long‐term production data. We therefore classified soil pedons on such sites, and tested thickness of mollic epipedon and other site characteristics as predictors of average range production. Specifically Mollisols under native range with 6‐ to 49‐ yr production records were examined at 14 sites in Montana, Wyoming, North Dakota, and Alberta, Canada. Sites ranged in precipitation, elevation, and latitude from 250 to 560 mm/yr, 595 to 2165 m, and 40 to 50° north. Mean annual standing crop production ranged from 0.4 Mg/ha on a coarse‐loamy, mixed, Aridic Haploboroll to 3 Mg/ha on a fine, montmorillonitic, Agric Cryoboroll. Thickness of mollic epipedon and Munsell color values were recorded for 30 samples per site. Multiple linear regression analysis showed thickness of mollic epipedon predicts long‐term production better than any other single factor tested, R2 = 0.39. Addition of precipitation data improved estimates of production and gave the equation: production (Mg/ha) = −1.34 + 0.023 [thickness of mollic epipedon (cm)] + 0.005 [precipitation (mm)], R2 = 0.72. Separation of sites by vegetation improved correlations between thickness of mollic epipedon and production, possibly because it grouped sites climatically. For Stipa/Bouteloua vegetated sites, production (Mg/ha) = 0.32 + 0.023 [thickness of mollic epipedon (cm)], R2 = 0.66. Depth to carbonates was also related to production.

Statistical Modeling of the Variability of Selected Colo Soil Properties

AbstractForty‐seven soils representing the Colo soil series (fine‐silty, mixed, mesic Cumulic Haplaquolls) as mapped on 0 to 2% slopes in the Upper Midwest were described and sampled to determine selected physical, chemical, and morphological properties to use in statistical modeling. The soils were sampled in Iowa (35 pedons), Nebraska (4), Missouri (4), Illinois (2), and Minnesota (2), and studied in the following groups: all Colo pedons, by master horizon, and by the presence or absence of postcultural sediments (PCS). The groups were statistically analyzed by using means, ranges, standard deviations, coefficients of variation, correlation coefficients, and multiple regression equations. The objectives of this study were to (i) characterize the Colo soil throughout its geographic range; (ii) stratify the data to study the relationship between selected soil physical, chemical, and morphological properties; and (iii) develop statistical regression models using several soil chemical and physical properties of one soil series. Ranges in soil properties such as particle size, hydrogen‐ion activity, and total carbon (TC) content are restricted by the limits of the official series used as guides in mapping. Therefore, these properties did not have as wide a range as other soil properties studied‐available, total (TP), organic (OP), and inorganic phosphorus (IP) or organic carbon/organic phosphorus (OC/OP) and organic phosphorus/total phosphorus (OC/TP) ratios which are not defined for the series. The Colo samples were stratified according to master horizon designations. TC, OP/TP, OP, and OC/OP means were highest in the A horizon and decreased with increasing depth in the profile. Soil properties used to define the series had a narrower range (e.g. particle size, TC amount) than other soil properties especially in the A horizon. Forty‐five percent of the pedons sampled had some evidence of PCS. The sand, silt, clay, and TC means were similar for those soils with or without PCS as were IP, OC/OP, and OP/TP. The ranges differed but were not as great as anticipated. If less than 50 cm thick, PCS should not be considered part of the mollic epipedon. Still all the soils studied had a mollic epipedon greater than or equal to 91 cm thick. Morphologically, the majority of the Colo soils described had an A‐B‐C horizon sequence. A B horizon was described to indicate “structural” alteration of original material. Alluvial‐derived soils are reported to be in an early stage of development and, therefore, should have little alteration of the original material. As indicated by some of the Colo soil properties, this assumption is not necessarily correct. As a result of this study, the genesis of some soils derived from alluvial sediments in the Upper Midwest is better understood.

Properties and Classification of an Eroded Soil in Southeastern Nebraska

AbstractPedons representing soil properties within three mapping units of the Wymore soil series were studied to determine if they were correctly classified and named. Present concept of the three units suggests that they differ in slope and/or erosion class, but that they are within the concept of fine, montmorillonitic, mesic Aquic Arquidolls. Pendons representing the noneroded, 0–2% slope unit (Wt) and the noneroded, 2–7% slope unit (WtC) exhibited properties that supported their present classification. However, 64% of the pedons sampled in the delineations representing the eroded, 2–7% slope unit (WtC2), and consequently the pedon representative of the WtC2 unit, had an epipedon that appeared to have been formed through tillage of a subsurface horizon. Established criteria for the mollic epipedon and the agrillic subsurface horizon were not evident. An ochric epipedon and cambic subsurface horizon existed in this pedon. These features plus a high base saturation, lack of pedogenic lime and mottling in the solum supported placement of the pedon representative of the WtC2 unit in the subgroup Aquic Dystric Eutrochrept. This pedon is representative of > 45,000 ha in the region of its existence.

A Century of Soil Development in Spoil Derived from Loess in Iowa

AbstractDuring the past century well‐drained soils have formed in leached loess spoil materials under prairie vegetation along railroad cuts in Iowa. The spoil material was deposited on an existing Tama Variant soil which reveals the effects of 100 years of burial.In 100 years' time a 31‐cm A horizon has developed in the spoil, available phosphorus recycling has been measured, and the translocation and accumulation of illuvial clay and fine silt has occurred. The organic carbon content reached a maximum of 2.6% and exceeds 0.58% to depths of 40 to 46 cm. This 100‐year‐old A horizon, however, does not meet the color criterion for a mollic epipedon. Organic carbon content seems to build up rapidly in the first 30 to 50 years of soil development. After this time a slower more steady‐state rate of increase seems to take place.In 100 years' time the buried soil shows a 1% decrease (from 2.6 to 1.6%) in organic carbon in the upper 20 cm. Most of this difference resulted from the degradation of fibrous organic matter after burial. Accompanying this loss of organic matter is an increase in bulk density, which has impeded soil water movement. This density contrast has enhanced the accumulation of illuvial clay and fine silts in both the lower portion of the 100‐year‐old soil and in the buried A horizon.

Relationships of Soils to Mountain and Foothill Range Habitat Types and Production in Western Montana

AbstractSoils at 23 sites representing eight western Montana mountain and foothill range habitat types were characterized and classified in accordance with Soil Taxonomy. The soils ranged from Borollic Calciorthids at the dry end of a moisture and soil development gradient to Pachic Cryoborolls on the moist end. Corresponding vegetation was a Stipa comata‐Bouteloua gracilis community on the dry end and a Festuca idahoensis‐Agropyron caninum community on the moist end. Soil taxonomic units and vegetation habitat types were ordered along the moisture gradient. Multiple linear regression analysis was used to model above‐ground dry‐matter productivity of the sampled sites. Eighteen significant variables were identified including thickness of the mollic epipedon, total soil organic matter, total N content, elevation, depth to free carbonates, estimated annual precipitation, aspect, solum thickness, summer soil temperature at 50 cm, percent coarse fragments in the A horizon, and extractable K. The thickness of the mollic epipedon was the variable most highly correlated with productivity (r=0.89**) and the best regression model accounted for 90% of the variability in total productivity between sites (based on 2 years' productivity data). Soil morphological characteristics proved more useful in models of site productivity than estimated climatic data or site nutrient data.

Holocene soils and soil-geomorphic relations in a semiarid region of southern New Mexico

Holocene soils of a semiarid area in southern New Mexico occur on terraces and fans in and adjacent to the mountains. The illustrative soils have formed in alluvium derived from rhyolite, monzonite, and sedimentary rocks, mainly limestone. A large arid basin occurs downslope from the mountains. In the arid-semiarid transition, the effect of a gradual increase in precipitation on soil morphology is shown by Holocene soils that sensitively reflect the precipitation. Where the parent materials contain little or no carbonate, a surficial noncalcareous zone and a reddish-brown horizon of silicate clay accumulation thicken mountainward as precipitation increases. The Bt horizon is underlain by the carbonate horizon, the upper boundary of which deepens mountainward. These orographic-depth relations and soil morphology support an interpretation that some of the clay (as well as the carbonate) is of illuvial origin. In high-carbonate parent materials, a noncalcareous zone has not developed and a reddish-brown horizon of clay accumulation has not formed. In upper horizons, organic carbon increases and color darkens towards the mountains. This causes a change in soils at the categorical level of soil order; Mollisols do not occur in the arid basin downslope, where nearly all Holocene soils are either Aridisols or Entisols. In the semiarid zone, however, most Holocene soils are Mollisols. Thick, dark A horizons have formed in many of these soils. The thickness of these horizons is attributed primarily to episodes of sedimentation during soil development. Some Holocene Aridisols also occur in the semiarid zone. Generally these are on narrow ridges, where the mollic epipedon has been truncated or did not form. In some terrains the soil-geomorphic relations are complex and Holocene soils may be above or at the same elevation as adjacent, much older soils. In such situations, when the morphological range of the various soils has been determined, soil morphology may be used to distinguish the Holocene soils and surfaces from their older analogs.

High‐altitude Photography in the Development of a Generalized Soil Map

AbstractState‐wide panchromatic photography of Minnesota was obtained at a contact scale of 1:90,000 and used for compiling a series of generalized soil maps. The taxonomic legend used was developed from selected concepts in Soil Taxonomy, generally at the subgroup level. The mapping rate is about one township per day with maximum use of stereo‐interpretation. Maps are compiled on composites of the U.S. Geological Survey 1:250,000 quadrangles. A concept of geomorphic regions is used to identify and isolate distinctive parent materials and topography. About 75 such regions are delineated. A concept of soil landscape units (SLU) was developed for mineral soils. These are viewed as collections of soil bodies having broad similarity in particlesize class of the control section and of material below the control section; in position and duration of the water table; and in the presence or absence of a mollic epipedon. For areas of organic soils, a taxonomic legend using suborder concepts was developed.